.bs {
    width: 70%;
    margin-top: 25px;
}
.bs th {background-color: #336699; color: white; padding: 0.8em;}
.bs tr {height: 35px;}
.bs td {border: 1px solid #336699; padding: 0.5em}
.centr {text-align: center}

 .menu {
            display: flex;               /*  Flexbox 布局 */
            justify-content: center;     /* 水平居中 */
            align-items: center;         /* 垂直居中 */
            margin-top: 10px;            /* 设置菜单顶部外边距 */
            height: 20px;               /* 给容器一个固定的高度，便于垂直居中 */
        }

        .menu_item {
            padding-left: 35px;
            padding-right: 15px;

        }
        .book-img-thumbnail {height: 50px}
        .auth-code {margin-top: 100px}
        .menu_item_right {float:right}
.menu_form {
    padding-left:100px;
    }